1. Field of the Invention
The present invention relates to a method for producing a semiconductor optical device.
2. Description of the Related Art
Patent Document 1 (Japanese Unexamined Patent Application Publication No. 6-21570) describes a method for producing a semiconductor optical device. According to this method, a first phosphorus-containing compound semiconductor layer and a second phosphorus-containing compound semiconductor layer are sequentially formed on a compound semiconductor layer serving as a base. The second phosphorus-containing compound semiconductor layer is composed of a material different from the material of the first phosphorus-containing compound semiconductor layer. A diffraction grating is subsequently formed in the first phosphorus-containing compound semiconductor layer and the second phosphorus-containing compound semiconductor layer is left on the projections of the diffraction grating. A heat treatment is then performed to make the second phosphorus-containing compound semiconductor layer on the projections of the diffraction grating fill the recesses of the diffraction grating.
Patent Document 2 (Japanese Unexamined Patent Application Publication No. 8-227838) describes a method for forming a fine pattern. According to this method, a diffraction grating is formed by an electron beam exposure method. In this method, a pitch of the diffraction grating is not restricted by the minimum travel length of an electron beam of an exposure system. As a result, the lasing wavelength of a distributed feedback (DFB) laser can be readily controlled.
Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2000-323461) describes a method for forming a fine pattern by a nano-imprint method. A mold for the nano-imprint method is placed on a mold substrate which is made of a transparent material and alignment marks are formed on the mold substrate. Alignment marks corresponding to the alignment marks formed on the mold substrate are also formed on a wafer. To accurately align the mold with the mold substrate, after the alignment marks are formed on the mold substrate, the mold for the nano-imprint method is formed with reference to the positions of the alignment marks of the mold substrate. By forming the mold and the alignment marks on the mold substrate, the alignment marks on the mold substrate and the alignment marks on the wafer can be simultaneously referred to when viewed from above the wafer through the mold substrate. By referring to these alignment marks in this way, the wafer and the mold are aligned relative to each other.